Premixing burners of this type are known, for example, from U.S. Pat. No. 4,932,861 to Keller et al. The air is put into rotation by the premixing burner, which is designed as a swirl body. This causes a reverse-flow zone in which the flame is stabilized. The flow velocity can be up to one hundred meters per second at the outer edge of the vortex generated by the premixing burner. In the inlet gaps gaseous fuel is injected, via a row of introduction openings, into the combustion air flowing from the compressor. These openings are, as a rule, evenly distributed over the entire gap, however, zones subjected to high thermal loads, so-called "hot spots", can occur in wall regions of the combustion chamber near the burner during the combustion of the gas mixture obtained in this manner. These zones are caused by the hot outlet gases which impinge at high flow velocities on the combustion chamber wall at the outer edge of the vortex. The "hot spots" can, furthermore, lead to the formation of undesirable oxides of nitrogen. The position of the "hot spots" changes with each type of operating condition, i.e. depending on whether the plant is operated at full load or part load or also, for example, as a function of the energy output of the fuel used.
Where improved cooling is provided to protect the combustion chamber wall, this is associated with disadvantages. In the case of convective cooling, a pressure drop occurs due to the necessary increase in the cooling air velocity and this reduces the efficiency. In the case of film air cooling, the film air is no longer available for combustion, so that the emission of oxides of nitrogen can be increased. It may be generally stated that the unnecessary cooling of zones which are not thermally loaded leads to increased emissions of carbon monoxide and that the exhaust gas temperature profile is impaired.